God’s supreme purpose for bringing sinners to salvation is to glorify His Son, Jesus Christ, by making Him preeminent in the divine plan of redemption. In the words of this text, it is God’s intent for Christ to be the first-born among many brethren.
In Jewish culture the term first-born always referred to a son, unless a daughter was specifically stated. Because the first-born male child in a Jewish family had a privileged status, the term was often used figuratively to represent preeminence. In the present context that is clearly the meaning. . . .